1. Field of the Invention
The present invention relates to a sifter frame used for a sifter for separating the particle sizes of powder particles such as flour and the like, and more specifically, to structure of an intimate contact type sifter frame used by being stacked in multi-stages to sift and separate powder particles.
2. Description of the Related Art
Sifters are conventionally used to separate the particle sizes of powder particles such as flour and the like. The sifter will be described below with respect to the separation of the particle sizes of flour by way of example.
Sifters are known in different types such as a plan sifter, square sifter and the like which have been used in the flour milling industry for a long time to separate the particle sizes of flour. At present, various types of sifters such as the modifications of the above sifters and intermediate type sifters (such as a junior type sifter and the like) are put into practical use. These sifters are fundamentally arranged such that powder having a small particle size is supplied onto the sifter and is caused to pass through the sifter downwardly while a multiplicity of stacked sifter frames are caused to make a circular motion to separate the particle sizes of the supplied powder. A reason why the flour sifter is composed of the sifter frames stacked in multi-stages as described above is to make a sifter area as large as possible, which is desirable to effectively separate flour by moving the flour on the surface of the sifter. To achieve this object, an area of the sifter per unit area of installation is increased to save an installation area so that the sifter is composed of sifter frames stacked in multi-stages and a sifter surface on which flour moves is formed so that the sifter surface vertically meanders in the sifter.
The sifter is usually composed of a group of stacked square sifter frames tightened from the upper and lower sides thereof or a group of sifter frames which are stacked to ten to twenty stages and accommodated in a sifter frame box called a box so that they are horizontally tightened and fixed and also tightened and fixed from the upper side thereof. Then, the box and the like are driven by a drive unit composed of an eccentric shaft provided with a balance weight and a drive shaft to make a circular motion within a horizontal plane at high speed.
Since sifter nets used for the sifter frames constituting the sifter are required to be checked and replaced at predetermined intervals, several hundreds to several thousands of the sifter nets must be always stored to cope with the requirement in industrial equipment. To facilitate replacement, conventionally employed is a sifter frame which has a structure for limiting a portion to be replaced only to a sifter net. That is, there are generally used a pair having a frame member of about 1 m.times.1 m (referred to as an outer frame) and a frame member having a sifter net stretched therein as an object to e replaced (referred to as an inner frame) with the inner frame being engaged with the outer frame. With the employment of this arrangement, even if several thousands of the sifter frames are required to be prepared and stored, since the outer frames can be repeatedly used, it suffices only to actually prepare the inner frames, which is preferable from the view point of industrial facility because the volume and weight of the inner frames to be stored are reduced and a replacing job can be simplified and labor can be saved accordingly.
A structure of the conventionally used sifter frame will further be described in more detail with reference to FIG. 32-FIG. 36.
The conventional type sifter frame shown in these figures has a combination type structure arranged such that a rectangular inner frame 500 (refer to FIG. 32) is fitted with the inner frame fitting portion of an outer frame 600 (refer to FIG. 33), the inner frame 500 having a sifter net 501 stretched over the upper surface thereof to separate flour to powder on a sifter (rough powder) and powder below the sifter (through: fine powder), and the outer frame 600 being in contact with the three circumferential sides of the inner frame and having a longitudinal path in an upward/downward direction (refer to FIG. 34).
The above inner frame 500 shown in FIG. 32 is composed of wood frame member 502-505 of, for example, wood for constituting a rectangular four-sided frame and a sifter net 501 having a predetermined shifting mesh and stretched over reinforcing wood bars 506, 507 formed to a cross shape and disposed inwardly of the rectangular frame member. Note, although not shown, a crimp net having a rough mesh is usually stretched below the sifter net 501 in parallel therewith and a cleaner such as, for example, a triangular flat cleaner having a hemispheric projection is movably interposed between the upper and lower nets so that clogging the sifter net 501 is prevented by causing the cleaner to beat the net when the sifter is in operation.
The outer frame 600 shown in FIG. 33 is composed of an inner frame fitting portion with which the above inner frame 500 is fitted in contact with (biased to) an outer side wall (outer block member) 610 as one of the four sides of the rectangular frame forming the outer block of the outer frame 600 and longitudinal paths 601, 602, 602 disposed outwardly of the inner frame fitting portion in an upward/downward direction along the inside of each of the remaining three sides except the side wall 610 of the above one side. Specifically, the outer frame 600 is composed of a pair of parallel inner side walls (frame members) 607, 607 disposed to form the above inner frame fitting portion, three inner frame fitting stand frames 604, 605, 606 fixed over the lower surfaces of the inner side walls 607, 607, a pair of outer side walls 608, 608 disposed separately to form the fine powder dropping ports 602, 602 to the outside of each of the above outer inside walls 607, 607, the outer side wall 610 disposed in contact with the outside of the inner frame fitting stand frame 606, an outer side wall 609 separately disposed to form a rough powder dropping port 601 (usually, called an over port) outwardly of the inner frame fitting stand frame 604, and a receiving plate (fine powder flowing plate) 603 provided as a bottom surface for introducing fine powder (through) having passed through the sifter net 501 of the inner frame to be fitted to the above right and left dropping ports 602, 602. Note, the inner side walls 607, 607 are fixed to the outer side walls 608, 608 at suitable positions through intermediate brackets 613, 613, and the inner frame fitting stand frame 604 is fixed to the outer side wall 609 through an intermediate bracket 615 in the same way. Numeral 614 denotes blocks disposed at four corners to close the unnecessary space portions in the outer frame as well as to increase the strength of a fitting structure in an upward/downward direction.
The receiving plate 603 is composed of a stainless steel sheet or the like fixed to the respective lower surfaces of the above inner frame fitting stand frames 604, 605, 606 by screws. With this arrangement, each of the right and left ends of the receiving plate 603 has a gap corresponding to the thickness of the stand frames 604, 605 between the lower surface of the inner side wall 607 and the receiving plate 603, and these gaps form slit-shaped fine powder dropping ports 617 for dropping fine powder onto the receiving plate 603 into the right and left fine powder dropping ports 602. Note, the receiving plate 603 is disposed substantially at the intermediate position in the upward-downward direction of the sifter frame in a bottom-lifted-state (refer to FIG. 35). With this arrangement, a space in which powder moves on the sifter net 501 of a lower stage sifter frame is provided with sifter frames are stacked. Note, when a direction is described below, a direction in which a pair of the fine powder dropping ports 602 is separated from each other is referred to as a right/left direction and a direction orthogonal to the right/left direction in a horizontal direction is referred to as a forward/backward direction.
A group of the sifter frames having the above arrangement can be constructed by stacking a multiplicity of the sifter frames in such a manner that the positions of the rough powder dropping ports 601 are successively reversed (alternately disposed) on the respective stages (refer to FIG. 35). Then, powder particles having moved (flown) on the sifter net 501 of a certain stage drop into the rough powder dropping port 601 of the inner frame 5 along the inclined surface 502a of the frame member 502 in contact with the rough powder dropping port 601 and move onto the sifter net of the sifter frame of the next lower stage. Further, fine powder having passed through the sifter net 501 drops onto the receiving plate 603 and further drops into the fine powder dropping ports 602 through the right and left slit-shaped fine powder dropping port 617.
Note, press beams 620, 620 are disposed between the outer side walls 609, 610 below the receiving plate 603 of the outer frame 600 so that the press beams 620, 620 extend to the upper surfaces of the inner side wall 607 and the frame member 504 (or 505) of the inner frame of the lower stage sifter frame to cover them in contact therewith (refer to FIG. 35).
Incidentally, the sifter is naturally required to securely prevent the mixture of rough powder with fine powder caused through the gap defined at the inner frame fitting position. For this purpose, the lower portion of the frame member 502 of the inner frame 500 is provided with a stepped portion as shown in FIG. 34(b) and the stepped leg portion 502b is engaged with the stepped portion 604a of the inner frame fitting stand frame 604 formed in correspondence with the outer frame to form seal portions.
FIG. 34(a) is an unfolded view for explaining a relationship between the outer frame 600 and the inner frame 500 fitted therewith, and FIG. 35 is an unfolded view for explaining a state that the sifter frames each arranged as described above are stacked with the rough powder dropping ports 601 thereof successively disposed alternately. Note, in FIG. 35, surfaces 700, 701 shown phantom lines serve as sealed surfaces for strongly pressing the inner frame 500 of lower stage the sifter frame downwardly by the upper stage sifter frame (outer frame 600) so as to increase the seal pressure of the above seal portions and at the same time to seal and partition a region (rough powder region) where rough powder flows from a region where fine powder flows (fine powder region). A suitable seal sheet is applied to the surfaces 700, 701 as necessary.
In the aforesaid conventional sifter, although a group of the sifter frames is composed of a multiplicity of the stacker sifter frames each arranged as described above to sift and separate flour, it is known that actually a slight amount of rough powder is mixed with fine powder.
Since the mixture of rough powder and the like caused by the conventional sifter is not ignored in a strict meaning regardless of a recent tendency that a powder product which has an increased added value or with which any rough powder and the like is not mixed at all is required, however, the sifter is desired to be further improved.
The inventors have discovered the following by examining a cause of the mixture of rough powder with fine powder, taking the present state mentioned above into consideration. That is, there is a problem that although the mixture of rough powder with fine powder in the conventional sifter frame is not caused on the above seal surfaces 700, 701 which are in intimate contact with each other under pressure, the mixture of them is caused at the portion where the frame member 502 is fitted with the inner frame fitting stand frame 604.
This will be described as follows with reference to FIG. 36. More specifically, first, although the portion where the frame member 502 of the inner frame in contact with the rough powder dropping port 601 is fitted with the inner frame fitting stand frame 604 of the outer frame is sealed by the engagement of the stepped portion 502b with the stepped portion 604a shown in FIG. 34(b), no pressure is directly applied to the portion from the upper and lower frames to make intimate contact therebetween. Thus, a problem arises in that they are not sufficiently sealed. Further, the following becomes apparent as a larger problem. That is, although brackets 616 provided to form the inner frame fitting portion of the outer frame is engaged with the extreme (front) end surfaces (surfaces facing to the rough powder dropping port) 504a, 505a of the right and left frame members 504, 505 of the inner frame to seal a fine powder region and a rough powder region, no pressure is applied to make intimate contact of the both surfaces of the fitting portion in the structure. More specifically, the direction of a horizontal force for causing both surfaces to come into intimate contact with each other is different 90.degree. away; from a vertical force for causing the upper and lower sifter frames to come into intimate contact with each other. On the other hand, a gap is inevitably produced between the surfaces due to a dimensional allowance in production and a dimensional variation caused by the elapse of time as an actual problem. Consequently, it is difficult to completely prevent the phenomenon that rough powder flowing on the sifter net as shown by a thick solid line 800 in FIG. 36 moves at random in the sifter frame which is violently vibrated when the powder is separated by the sifter and enters a gap between the above extreme end surface 505a and the bracket 616 as shown by a thick dotted line 801 in the figure. Further, since it is also inevitable that a gap is produced between the outside surface of the frame member 505 (504) of the inner frame and the inside surface of the inner side wall 607 of the outer frame, the rough powder having entered the above gap further moves and enters the fine powder region as shown by dotted lines 802, 803, by which the aforesaid mixture is caused.
Further, since the frame member 502 in contact with the rough powder dropping port of the inner frame is not directly pressed in an upward/downward direction by the outer frame of the upper/stage sifter frame being stacked, a force for causing the both surfaces of the frame member 502 and the above member (inner frame fitting stand frame 604) to come into intimate contact with each other is weakened in the vicinity thereof. As a result, since it is inevitable that a gap is produced between the frame member 502 and the stand frame 604 by the vibration of the sifter frame, rough powder also enters the fine powder region at this portion.
The problem that rough powder enters the fine powder region though the gaps between the confronting surfaces to which the above intimate contact force is not applied can be of course solved by providing a sifter frame of an inner frame and an outer frame which are integrally arranged each other so that the sifter frame is not divided into the inner frame and the outer frame. With this arrangement, however, the aforesaid requirement cannot be satisfied from the view point of the industrial equipment for limiting the portion to be replaced of each fo the sifter frames, which can amount to several thousands to an area as small as possible in order to that storing volume is reduced and labor for a replacement job is saved.
Further, there is a possibility that the influence resulting from vibration can be prevented so as to avoid the aforesaid unacceptable matters by the employment of a method of fixing the inner frame to the outer frame by means of tightening means such as bolts or the like, When such a method is employed, the attachment and detachment of the inner frame to and from the outer frame is very time consuming, by which the device of partially replacing the sifter frame is made quite useless.
An object of the present invention is to provide a novel powder separating sifter frame by solving the above various problems which is capable of reducing a storing volume by limiting a portion of a sifter frame to be prepared and stored as well as satisfying a requirement for saving labor needed for a replacement job and securely preventing the mixture of rough powder with fine powder which has been sometimes caused by a conventional sifter frame.